The loudspeaker module is an important acoustic component in portable electronic devices. As an energy conversion device, it is used to complete the conversion between an electrical signal and an acoustic signal. A conventional loudspeaker comprises a vibration assembly and a magnetic circuit assembly, most magnetic circuit assemblies comprise an internal magnetic circuit assembly and an external magnetic circuit assembly, and the external magnetic circuit assembly surrounds the periphery of the internal magnetic circuit assembly. During the assembling of loudspeakers, it is required to magnetize the internal magnetic circuit assembly and the external magnetic circuit assembly, and make the polarities of the internal magnetic circuit assembly and the external magnetic circuit assembly opposite.
Presently, the process of magnetizing such multi-magnetic-circuit magnetic circuit assemblies comprises the following steps, as shown in FIG. 1a, FIG. 1b and FIG. 1c: 
the first step: an un-magnetized internal magnetic circuit assembly 12 is magnetized by an internal magnetic circuit magnetizing coil 40 to form an internal magnetic circuit assembly 10 after the magnetizing finishes. In the internal magnetic circuit assembly 10, the upper end is the N pole and the lower end is the S pole (only if the electric current direction is as shown in the figures; if the electric current direction is opposite, the magnetic poles after magnetizing are also opposite);
the second step: an un-magnetized external magnetic circuit assembly 22 is magnetized by an external magnetic circuit magnetizing coil 50 to form an external magnetic circuit assembly 20 after the magnetizing finishes. In the external magnetic circuit assembly 20, the upper end is the S pole and the lower end is the N pole; and
the third step: the internal magnetic circuit assembly 10 is fixed to the external magnetic circuit assembly 20 using an adhesive, to form the finished product of magnetic circuit assembly 30.
The above process for magnetizing multiple magnetic circuits in which the magnetic circuit assemblies are magnetized first and then adhesively fixed has the following defects:
first, since part of the magnetism will be eliminated at a high temperature, only the adhesives that have a relatively low solidification temperature can be selected to adhesively bond the internal magnetic circuit assembly and the external magnetic circuit assembly. The long solidification duration of these adhesives results in low production efficiency of multi-magnetic-circuit magnetic circuit assemblies;
second, the adhesives that have a relatively low solidification temperature usually have a relatively small adhesion force, which cannot satisfy the requirements on the products. Moreover, available adhesives that have large adhesion force and low solidification temperature are few and expensive, which increases the production cost of the products; and
third, because after the magnetizing the polarities of the internal magnetic circuit assembly and the external magnetic circuit assembly are opposite, they have a certain attraction force therebetween, which greatly increases the difficulty in the step of adhesive bonding, and further reduces the production efficiency.